Clinicians Pocket Reference, 11th Edition

Defining Pain and Educating the Patient

The International Association for the Study of Pain defines pain as an "unpleasant sensory and emotional experience associated with actual or potential tissue damage." Pain is the most common symptom that brings patients to see a physician, and it is frequently the first alert of an ongoing pathologic process. Whenever possible, inform the patient beforehand about the nature and the degree of pain to be expected during a hospital stay. Make the pain control options clear during and after hospitalization so that the patient will have realistic expectations.

Classification of Pain

Somatic Pain

A well-localized constant, achy area in skin and subcutaneous tissues and less well-localized in bone, connective tissues, blood vessels, and muscles. Examples are incisional pain, bone fractures, bony metastasis, osteoarthritis and rheumatoid arthritis, and peripheral vascular disease.

Visceral Pain

Poorly localized, crampy, diffuse, and deep sensation originating from an internal organ or a cavity lining. Examples are bladder distention and spasms, intestinal distention, inflammatory bowel disease, hiatal hernia, organ metastasis, and pericarditis.

Neuropathic Pain

A poorly localized, electric-shock-like, lancinating, shooting sensation originating from injury to a peripheral nerve, the spinal cord, or the brain. Examples are diabetic neuropathy, radiculopathy, postherpetic neuralgia, phantom limb pain, and tumor-related nerve compression.

Adverse Physiologic Effects of Pain

Table 14 1 shows adverse effects of pain as they relate to specific organ systems.

Assessing Pain

Pain assessment has physiologic, emotional, and psychological aspects. Ask the patient about discomfort. Conduct a detailed history interview to gather information about the patient's pain.

Information about what relieves the pain and what makes it worse is as important as how long the pain lasts. Is the pain constant or intermittent? Does it have any precipitating factors? Does the pain radiate to a specific extremity, or is it referred from an internal source? An example of a pain radiating to a limb is lower back pain with associated right or left leg radiation. An example of referred pain is a ureteral calculus referring pain to the ipsilateral testicle. Are there any accompanying symptoms, such as nausea, vomiting, or headache?

In addition to a thorough physical exam, consider using a pain assessment instrument or rating scale to further stratify the level of pain.

Visual Analog Scales

Often called the "fifth vital sign." Ask the patient to indicate on a visual scale the intensity of pain. These scales are particularly useful for assessing pain management interventions. Examples of commonly used visual scales are shown in Figure 14 1.

McGill Pain Questionnaire:

The MPQ (Malzack RR: The McGill Pain Questionnaire: Major properties and scoring methods. Pain 1975;1:227 299) is a checklist of words describing symptoms. Analyze scores in various sensory and affective dimensions to identify the quality of pain. Consider using this tool in the detailed management of pain syndromes.

Psychological Evaluation:

A psychological evaluation is indicated if medical evaluation does not reveal an apparent cause of pain. Two tools frequently used for evaluating chronic pain and depression are the Minnesota Multiple Personality Inventory (Hathway SR and McKinley JC: MMPI. University of Minneapolis Press, Minneapolis, 1989) and Beck Depression Inventory (Beck AT, Steer RA: Internal consistencies of the original and revised Beck Depression Inventory. J Clin Psychol 1984;40:1365 1367). Use these questionnaires to determine the patient's psychological status and to his or her behavior and response to pain and its management.

Electromyography and Nerve Conduction Testing:

Used to differentiate neurogenic from myogenic causes of pain and to confirm a diagnosis of nerve entrapment, neural trauma, or polyneuropathy.

Thermography:

Under normally circumstances, heat from body surfaces is emitted in the form of infrared energy; this emission is symmetrical in homologous areas. Neurogenic pathophysiologic changes result in asymmetry. This infrared energy can be measured and displayed: Hyperemission indicates an acute stage and hypoemission a chronic stage.

Diagnostic and Therapeutic Neural Blockade:

Neural blockade with local anesthetics used in the diagnosis and management of both acute and chronic pain.

Pain Management (Acute vs Chronic)

The goal of pain management is to provide the patient adequate relief with minimum side effects (eg, drowsiness). Always begin therapy with the lowest dose of any medicine that provides significant relief.

Pain management can be generally divided into:

• Pharmacologic
• Nonpharmacologic
• Combinations according to patient response and compliance

Pharmacologic

The World Health Organization has made specific recommendations concerning pain management. These principles apply primarily to cancer pain but can be used in any clinical setting. Start at step 1 and advance to the next level on the basis of the patient's response.

Step 1: Nonopioid agents (eg, NSAIDs, acetaminophen, aspirin, COX-2 inhibitors)

Step 2: Weak opioids (codeine, oxycodone) or opioid-like agents

• Use concurrently with step 1 agents (eg, oxycodone, hydrocodone combinations)
• Weak opioids as single agents (immediate-release codeine, propoxyphene)
• Opioid agonists and antagonists (pentazocine, butorphanol)
• Other agents such as ketorolac or tramadol

Step 3: Strong opioids. Controlled-release oxycodone, morphine, or fentanyl

Step 4: Multimodal approach (eg, neurolysis)

Specific pharmacologic agents are reviewed in the following section and in Table 14 2 with additional information in Chapter 22. Supplemental agents can enhance the effects of analgesics and allow dose reduction of some agents.

Nonopioid Analgesics:

A multimodal approach may involve pharmacologic and nonpharmacologic methods. Aspirin, acetaminophen, and NSAIDs are the principal nonopioid analgesics used to manage mild and moderate pain. NSAIDs are primarily cyclooxygenase inhibitors that prevent prostaglandin-mediated amplification of chemical and mechanical irritants of the sensory pathways. Short-term (maximum 5 d of use) perioperative use of ketorolac (Toradol) can reduce pain medication requirements. Side effects: Possible hepatotoxicity (large dose of acetaminophen); stomach upset, nausea, dyspepsia, ulceration of gastric mucosa; dizziness; platelet dysfunction; exacerbation of bronchospasm; acute renal insufficiency (aspirin and NSAIDs).

Opioids:

Attach to opioid receptors, which are responsible for their analgesic effect. Side effects: In acute pain, nausea and vomiting are the most common side effects and usually resolve with time or antiemetics. In chronic pain, constipation is the most common side effect and persists until treatment cessation. Other side effects include sedation, miosis, and dizziness with smaller doses. Larger doses can precipitate respiratory depression, apnea, circulatory arrest, comma, and death. These more serious side effects may necessitate supplemental oxygen therapy, pulse oximetry monitoring, and close patient supervision. Opioids can be taken orally or parenterally or by the neuroaxillary route (intrathecal/epidural). Opioids are available in short- (q4h) and long-duration forms (eg, q12h, q24h). Opioids can also be given IV as a patient-controlled analgesia (PCA). Comparison of opioids can be found in Table 14 2.

Antidepressants:

Work well as adjuncts and are an appropriate consideration mostly for chronic pain associated with diabetic neuropathy, postherpetic neuralgia, and chemotherapy. Side effects: Antimuscarinic effects (dry mouth, impaired visual accommodation, urinary retention), antihistaminic (sedation), and alpha-adrenergic blockage (orthostatic hypotension).

Neuroleptics:

Used to treat patients with agitation and psychological symptoms. Side effects: Extrapyramidal and neuroleptic drug symptoms; mask-like facies, festinating gait, cogwheel rigidity (bradykinesia) managed with benztropine or diphenhydramine.

Anticonvulsants:

Suppress spontaneous neural discharge. Side effects: Bone marrow depression, hepatotoxicity, possible ataxia, dizziness, confusion, and sedation (at higher doses).

Corticosteroids:

Antiinflammatory agents. Side effects: Hyperglycemia, increased risk of infections, peptic ulcer, osteoporosis, HTN, myopathy, Cushing syndrome.

Local Anesthetics:

Bind to sodium channels, exerting effect on the cellular level. Effect usually localized to the area where the drug is injected. Side effects: Relatively few side effects. Allergic reactions usually due to PABA-like preservatives in the solution and not the agents themselves. Toxicity (usually due to overdose) includes tonic clonic seizures, respiratory arrest, and subsequent cardiovascular collapse.

Benzodiazepines:

Used to manage anxiety and muscle spasms associated with acute pain. Side effects: No analgesic effects and must be used with caution because of abuse potential.

Nerve Blocks or Neurolysis:

Destruction of nerves. Side effects: Permanent nerve damage

Nonpharmacologic

Physical Therapy:

Heat and cold can provide pain relief by alleviating muscle spasm. Heat decreases joint stiffness and increases blood flow; cold vasoconstricts and reduces tissue edema.

Osteopathic or Chiropractic Treatment:

Physical manipulation can relax soft tissues, increase range of motion, and alleviate pain. Biweekly or monthly treatments are recommended and are best for chronic pain. Acute treatment minimizes musculoskeletal pain.

Radiation:

Beneficial in management of cancer pain (eg, bony metastasis).

Psychological Intervention:

Cognitive therapy, behavioral therapy, or biofeedback relaxation technique and hypnosis. Pain is often associated with depression, especially when it becomes chronic.

Acupuncture:

Needles are inserted into discrete anatomically defined points or meridians and stimulated by mild electric current. This method is believed to release endogenous opioids.

Electrical Stimulation of Nervous System:

Analgesia is achieved using various methods of treatment. The three methods are:

1. Transcutaneous electrical stimulation (TENS) with electrodes applied to skin.

2. Spinal cord stimulators: Electrodes connected to an external generator into the epidural space. Patient is under general anesthesia and is awakened half-way through the procedure in the lateral recumbent position. The patient is asked specific questions, and the programming is adjusted accordingly. The patient is put back under anesthesia, and the surgeon can close the skin.

3. Intracerebral stimulation with electrodes implanted in the periaqueductal or periventricular area.

Patient-Controlled Analgesia (PCA)

Most commonly used after surgery. Allows the patient to self-administer doses of narcotics with an IV pump. The patient manages the pain as soon as he or she feels it coming on, thus avoiding the peak and trough of a narcotic dosing regimen that can lead to extremes of pain or risk of oversedation. The pain management team can titrate the dose of the drug as required with a computerized system that controls the total dose and the interval between doses with or without a continuous basal infusion. PCA duration varies according to procedure and patient response (eg, gynecologic procedures, 1 2 d; bowel operations, 2 5 d; thoracotomy, 4 6 d). Reduce dose in elderly (1/3 2/3), and consider discontinuation of PCA when patients are able to take analgesics PO.

PCA Ordering Parameters

Table 14 3 shows examples of PCA orders.

• Dose: Number of milliliters (typically morphine concentration or its equivalent) given on activation of button by patient
• Lockout: Minimum interval of time in minutes between PCA doses
• Hourly Max: Maximum volume (milliliters) that machine will administer in an hour
• Basal Rate: Continuous infusion rate may be programmed in addition to the bolus dosing; not recommended unless a qualified member of the anesthesiology department pain team has evaluated the patient. Basal infusions increase risk of significant respiratory depression and should be monitored more closely with hourly respiratory checks.
• Nursing PRN Bolus: Number of milliliters nurses can administer at their discretion in addition to PCA dose for breakthrough pain.

PCA in Renal Failure (Nonencephalopathic Patient):

Use fentanyl or hydromorphone only, avoiding morphine and meperidine because of their renal excretion.

Load with fentanyl 25 mcg or hydromorphone 0.5 mcg IV in postanesthetic care unit and repeat every 5 10 min until patient is comfortable.

Maintenance: PCA dose 1 mL; lockout 6 min; hourly max 3 5 mL